Dual frequency rotatable joint



A. E. sMoLL 2,853,681

DUAL FREQUENCY ROTATABLE JOINT Filed Jan. 50, 195s Sept. 23, 1958 /Hen E. Smoll,

,by www N i s Attorney.

United States Patent DUAL FREQUENCY ROTATABLE JOINT Allen E. Smoll, Syracuse, N. Y., assignor to General Electric Company, a corporation of New York Application January 30, 1953, Serial No. 334,243

13 Claims. (Cl. S33-6) The present invention relates to rotatable-joint structures for ultra-high-frequency wave energy and, more particularly, to such rotatable joints that are adapted for operation with waves of two different frequency values.

In a copending application of A. E. Smoll and D. L. Smith, Serial No. 287,128, now Patent No. 2,719,230 filed May l0, 1952, entitled Dual Frequency Antenna, and assigned to the assignee of the present application, an ultra-high-frequency antenna is described and claimed, which is adapted to be operated with electromagnetic waves of two different ultra-high-frequency values having a frequency ratio of about 3:1. Such an antenna is suitable for and is therein disclosed in connection with a marine-navigation radar system. Accordingly, the antenna is ship-borne and mounted for continuous rotation about a predetermined axis and selectively operable at one or the other of the different frequencies according to the location of the ship on the open sea where operation at one frequency is advantageous, or in harbors and relatively narrow channels where operation at the other frequency is advantageous.

The rotatable joint of the present invention is especially well suited for transmitting waves of the widely differing frequencies between the rotatable antenna and the stationary transmitting and/or receiving apparatus of the radar referred to hereinabove. It will'be understood, however, that other uses for the rotary joint of this invention will be apparent to those skilled in the art.. Such uses can be found in multiple-receiver radar systems havingvseparate antennas for the individual receiving systems, as for example, radar systems having associated interrogation equipment.

Heretofore, ultrahighfrequency rotary joints or couplings for multi-frequency operation have been proposed of which one known type employs a double-concentric line for isolation of the individual frequencies, while another uses cavity resonators at the opposite ends of a single coaxial line or waveguide to operate as filter elements for separating the individual frequencies. While the latter-mentioned type overcomes an inherent defect of the former type that resides in the fact that, for operation with more than two individual frequencies, the multiple coaxial construction is complicated and unwieldy, the cavity resonator type itself is relatively impractical because of the odd geometrical forms and shapes that the resonators must assume making it diicult to predict with certainty the operating mode. Also, since the power must traverse the resonators, the power-handling capacity is necessarily limited to avoid arcing and attendant loss of signal.' Furthermore, the known types of rotary joints heretofore described are useful for operation with different frequencies where the individual frequencies lie 1 within a relatively small band of frequency values, e. g., where the frequencies differ from each other only by as much as 10%.

An object of the invention is, therefore, to provide a novely and' improved rotatable joint operable with electromagnetic waves of widely diiferent frequency values,

2,853,681 Patented Sept. 23, 1958 "ice . as to prevent waves of either frequency from being supplied from the source of one frequency to the source of the other frequency.

Another object of my invention is to provide a joint of the type mentioned having improved means to effect decoupling of the individual supply circuits, thereby to reduce dissipation of the energy.

Another object of the invention is the provision of an improved rotatable joint operable with waves of different frequency values and which is so designed as to prevent waves o f either frequency from vbeing supplied from a common source to the translation apparatus of the other` frequency. More specifically, an object of my invention is to provide such a joint having means to effect decoue.

pling of the two circuits connected to said joint for supplying to and receiving therefrom waves of ultra-high-fre quency energy, thereby to reduce dissipation of the energy of either frequency in the circuit of the other frequency.

Briefly stated, in accordance to yone aspect of my invention, the waves of one frequency are eectively isolated from the sources and/or the receivers of waves of the other frequency by means of a common coaxialline transmission system having relatively rotatable parts capable of transmitting waves of both frequencies,` to which system are connected a waveguide coupling for connecting the system to a source or receiver of one frequency and a coaxial coupling for connecting said system to a -source or receiver of the other frequency,y the couplings being spaced by transmission line `lter sections adapted to pass one frequency and reject the other; the system further including an additional filter at the junction of the rotatable .and stationary parts of the common coaxial system adapted to minimize radiation energy of either frequency through the junction.

The novel features which I believe to be characteristic of my invention are set forth withparticularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and 'advantages thereof, may best be understood by reference, tothe following description taken in connection with the accompanying drawing, the

single figure of which is a block diagram of a system incorporating novel features of the invention and including a longitudinal cross sectional view of a rotatable coupling arrangement constructed in accordance with the sources 13 and 15 of wave energy frequencies fi and f2,

respectively, and respective relatively rotatable utilization Vdevices 17 and 19 therefor. In one practical embodiment, the rotatable coupling of this invention, asrnoted hereinabove, and as described in the above-mentioned copending application, is employed in a marine-navigation radar in which the utilization devices 17 and 19 are in the form of a single antenna adapted to be energized by waves of the first frequency, f1, which, for example, may be of the order of 3,000 megacycles per second, and also by waves of the second frequency, f2, which may be of the order of 9,000 megacyclesper second.` For the purpose of this description, the use of the rotatable coupling in such a system will be taken as illustrative, it being clearly understood, however, that other uses are possible, as for example, in systems where the utilization devices 17 vand 19 are separate antennas. It will be understood further, that although the invention'is here described as applied to a transmitter unit, it can be used, 'withiequal effect,

in connection with a receiver unit or with a transmitreceive unit, as desired.

As shown, the coupling 11 is comprised of relatively Stationary and rotatable parte 2 1 and 23. respectively, which are interconnected. by a section of coaxial transmission line 2,5 ofany suitable lengthl and having coaxially disposed inner and outer conductive members Z7 and 29, respectively. The conductors 27 and 29 may be of circular cross section having respective `diameters which are dimensioned to support the principal TEM mode for the frequencies f1 and f2.

The coaxial line 25 is divided, as by a pair of axially spaced junctions or gaps of which a first junction or gap 31 spaces the fixed inner conductor 27 from a relatively moyable inner conductor 2/8, and a second junction or gap 33. spaces the fixed outer conductor Z9 from a relatively movable outer conductor 30. lt will be understood thatthe upper part23 is capable of rotation relativel to the, lower part, 21 by the operation of any suitable driving means.l (not shown) well known to those skilled in theffa t," The lower part 2,1 may bel relatively fixedly supported byany suitable means (not shown). For reasons that will become more apparent as the description proceeds, the verticalV spacing of the junctions 31. and 33, is a singularly advantageous feature of the invention inasmuch as'the usualproblems associated with the design and construction` of suitable filter elements are thereby minimizedt I The stationary partrZl of the coaxial line Z isV preferably coupledy tol the source 1,3V of the wave energy of frequency f1 by means of a stub-supported coaxial T-joint comprising a short section of coaxial line 35 that is coupled tothe part 21 through a suitable opening in the outer conductor 2,9.' Therequired impedancematch for the source13V ofthe frequency. f1 may be provided by a conventional stub, support 37 short-circuited at one end as by a conductive plate member 39 and having a suitable length, as measured from the junction of the T-joint to the shorting plate 39 that ycan be determined in accordance with well-known principles, toprovide a desirable voltage-standing-wave ratio. e

The coupling of the source jo f the wave energy of the frequency f2 is preferably effected by means of asection of rectangularl waveguide 41, which, as: shown, is coupled to the coaxial linezjbyrmeans -ofa conventional waveguide-to-coaxialtransition. Such a. transition cornmonly; includes an 'enlarged-inner-conductor portion 43` extending transversely throughthe wave guideand a quatter-wavelength short-circuited section 45. of waveguide whichncooperate in awell-known manner to improve the impedance match.l The waveguide 41 is desirably dimensioned` below cutoff. for waves ofthe frequency f1 while passing freely waves of theA frequency f2.

To isolatethe source 13 fromrwave energy of the frequency f2 originating at source 15, I provide a filter section 47 betweenthe' T-joint'` 35 and the coaxial-towaveguide transition 43,45, The filter 47.is designed to pass waves of the frequency f1 and to reject wavesof the frequency f2, and to that end, itoisforrned of a pair of radial transmission lines 4,9.and51` in the form of annular grooves each having a depth substantially equal to one quarter wavelength .atthe frequency f2, the centers of the grooves being. spaced a distance of about one-halfA wavelength atthesame frequency, The distance from the groove 51 to the waveguide 41 is desirably adjusted in thek assembling ofthe coupling so as to provide suitably matched impedances betweenthelter and the wavegni f 1, Alsohth'e width ofthe gITOOVes 49, 51 isY made suicientlyi large` to minimizev the danger of"r electrical breakdown.

Y Filter sections of the typehere described are well known and operateas band-rejection filters; the filter 47 tending to reject a bandrof frequencies peaked ,atthe frequency f2 andto pass otherfrequencies including the frequency-f1. It will thus .beseen that wave energy., at the frequency f1,

applied from source 13 to T-junction 35 traverses the filter 43 and is rejected by the waveguide 41, which, as noted above, is dimensioned below cutoff for waves of frequency f1. Accordingly, waves of frequency f1 are propagated by the coaxial section 25 toward the junctions 31 and 33, without loss to the source 15. Also, wave energy at the frequency f2 is coupled into the coaxial section 25 from the waveguide 41 and source 15, and, being rejected by the filter 47, is propagated toward the junctions 31 and 33 of coaxial section 25, without loss to the source 13.

At the junction 33 between the stationary and rotary parts of the joint 11, l provide a filter 53 that is adapted to pass wave energy of both frequencies f1 and f2 axially across the junction gap 33 while minimizing the passage of energynof either frequency radially through the gap. As shown, the filter 53 is comprised of a tandem connection of a short-circuited quarter-wavelength transmissionline section 55 and an open-circuited quarter-wavelength transmission-line section-57, the latter being folded back along the former to provide a compact non-contacting high-frequency short circuit at the peripherally extending gap defined by the adjacent ends of the outer conductors 29 and 30 of the coaxial transmission line 25.

To form the transmission-line sections 55 and 57 of the filter 53, the end of the outer conductor 29 adjacent the junction 33 is provided with a radially-extending ange member S9, which carries* on the upper edge thereof anA inner sleeve 61 and Va coaxially disposed outer. sleeve 63, each said sleeve being.` substantially one-quarter wavelength long at the frequency f1, the sleeve 63 being externally threaded, as at 65, over a portion of its length. The sleeve 61 extends in spaced parallel nesting relation to the, rotatable outer conductor 30 and the sleeve 63 is so` disposed on the upper edge ofthe ange 59 as to dene therewith a peripherally extending shoulder 67 adapted to seat the inner, relatively stationary race 69 of a suitable conventional ball-bearing assembly 71'. The race 69 can be securely fastened in position as by an internally-threaded nut 73 in engagement with the threaded portion 65'of thesleeve 63;

A radially extending 'ange 75,.forn1edl on the rotatable outer conductor 30 andspacedfrom the gap-33' a distance substantially one-quarter wavelength a-t the frequency f1,

is provided at the periphery thereof 'with a downwardly projecting cup-shaped member 77 of which the inner surface is recessed as at 79 and threaded as at 81. The surfaces of the recess 79 provide a shoulder on which the movable race 83 of the bearing assembly 71 is seated and. securedas by an externally-threaded nut 85; The nesting; relation of the relatively stationary androtatable parts is such that the inner surface of the flange andV the upper edge of the sleeves 61 and 63'are spaced to de.- ine agap 87.

It will thus be seen that the portion of the rotatable outer conductor 30 depending from the ange 75 and the sleevel lcooperate to provide the open-circuited quarter wavelength transmission-line section 57, and the sleeves 61 and 63 `cooperate to dene the short-circuited quarterwavelength transmission-line section 55 connectedV in tandem to the section 57 through the. gap 87.

In accordance with the well-known transmission-line theory, andrecalling that .the frequency values, f1 and' f2 related in accordancewith f2=3f1, so that the. lengths ofthe sections 55 and 57 are three-quarters of a wavelength atthe frequency f2, a minimal impedance for wave energy of both frequencies f1 and f2 is presented atthe gap 33the current across the gap being a maximum, while the impedance atthe gap 87 is maximizedforboth frequencies. This desirable vresult makes possible relatively lossless transfer of energy of either or both frequencies from the stationary to the rotational parts of. the outer conductor coupling.

As noted above, .the rotatingjoint foi-the inner conf..

ductor 27 ofv the coaxial line, is preferably: axially.. spaced.

from the rotating joint for the outer conductor 29, thereby to overcome the problem of spacing relatively large numbers of machined parts in a relatively small space, which is encountered where the respective inner and outer rotating joints are located at the same vertical position. It will also be apparent from the following description that the inner conductor rotating joint beyond the output coupling to the utilization device 19, the inner conductor rotating joint is called upon to operate only for one frequency, namely the frequency f1.

To form the inner conductor rotating joint, the stationary inner conductor 27 is provided with an enlarged diameter portion 89 starting at a point within the output coupling to the utilization device, which, as will be explained hereinbelow, is preferably a below-cutoff waveguide section 91 adapted to transmit freely waves of frequency f2 and to reject waves of frequency 71.

The inner-conductor portion 89 is formed as an openended hollow cylinder 93 of a length substantially equal to one-half wavelength at the frequency f1. A reentrant stub 95 is coaxially disposed within the cylinder 93 and projects upwardly for a distance slightly less thanonequarter wavelength at the frequency f1. An axial well 97 is formed in the upper part of the stub 95 to receive a bearing pin 99 secured to the bottom end of the rotating inner conductor 28. If desired or required, lubrication of the pin bearing may b'e had by coating the pin 99 with a suitable lubricant such as graphite powder.

The operation of the inner-conductor rotating joint assembly just described follows from well-known transmission-line theory. The sleeves 93 andthe stub 95 and inner conductor 28 assembly cooperate to define a cascade connection of two quarter-Wavelength sections of transmission line, one section being short-circuited by the closed end of the sleeve 93, the other section being open-circuited. Since the bearing is at the junction 31 of the quarter-wavelength sections, an open circuit appears thereat, which open circuit is transformed by the upper quarter-wavelength section to a short circuit at the gap 101 between the open end of the sleeve 93 and the adjacent vend of an enlarged-diameter extension 103 of the rotatable inner conductor 28. It will thus be clear that energy at the frequency f1 rejected by the waveguide 91 and traversing the coaxial portion extending thereabove is substantially completely passed through the coaxial output coupling 105 to the utilization device 17 with practically no loss of said energy through the bearing gap 31.

To direct the energy of frequency f2 to the utilization device 19 therefor, an output coupling is provided in the form of a waveguide 91 dimensioned below cutoff for frequency f1 and a coaxial-to-waveguide transition gen erally similar to the corresponding elements described hereinabove in connection with the waveguide 41. The transition and the waveguide 91 operate in the manner described above so that the energy of frequency f2 is freely propagated through the waveguide 91, energy of frequency f1 being rejected thereby.

The energy of frequency f1, rejected by the waveguide 91 is passed by a filter 107 of substantially the same type as described above in connection with the lter 47 on the stationary part 21. The filter 107, it will be understood, operates to reject wave energy of frequency f2, and as a result of the operation of the below-cutoff waveguide 89 and the lter 93, isolation of the utilization devices 17 and 19 with respect to the frequencies f2 and f1, respectively, is effected.

The output coupling 105 can be in the form of any suitable conventional co-axial-line section having a tapered inner-conductor 109 coaxially supported within a cylindrical outer conductor 111 for eiciently conducting the energy of frequency f1 to the utilization device 17.

An important advantage of my invention is that a single coaxial-line rotatable transmission joint can be employed to conduct waves of two or more widely different ultra- 6 high-frequency values under relatively Yl'niglI-po'werv c'orld ditions. Furthermore, the design of the lters is considerably simplified inasmuch as certain ones need be designed for operation with but one of the two different.

tively rotatable coaxial line section, each having respec tive outer conductors and coaxially disposed inner conductors dimensioned to transmit ultra-high-frequency waves of two integrally related frequency values, adjacent ends of said outer conductors being supported in spaced relation to define an outer-conductor junction, adjacent ends of said inner conductors being supported in spaced relation to deiine an inner-conductor junction, said inner conductor junction being axially spaced from said outerconductor junction, means connected to said stationary line section coupling thereto wave energy of said two frequency Values, a first output coupling connected to said rotatable line section and disposed between said outer-conductor junction and said inner-conductor junction for waves of one said frequency value, a second output coupling connected to said rotatable line section at a point thereon opposite said inner-conductor junction relative to said outer-conductor junction, and lter means at each said junction adapted selectively to pass waves of predetermined ones of said frequency values and to minimize loss of said waves through said junctions.

2. An ultra-high-frequency Wave transmission system comprising a first source of ultra-high-frequency wave energy having a predetermined frequency, a second source of ultra-high-frequency wave energy having a predetermined frequency harmonically related to the frequency of said first source, utilization means adapted for operation with wave energy of either of said frequencies, said utilization means being supported for rotary movement relative to said rst and said second sources, and coaxial transmission-line means interconnecting said sources and said utilization means, said transmission-line means including rotary coupling means having unitary iilter means associated therewith, said filter means comprising ra |coaxial transmission-line section an effective length corresponding to one-quarter wavelength at one said frequency and three-quarters wavelength at the other said frequency, whereby waves of both said frequencies are transmitted thereby with substantially no attenuation.

3. An ultra-high-frequency Wave transmission system comprising a first source `of ultra-high-frequency wave energy having a predetermined frequency, a second source of ultra-high-frequency wave energy having a predetermined frequency related to the frequency of said first source according to the ratio l 3:1, utilization means adapted for operation with wave energy of both said frequencies, said utilization means `being supported for rotary movement relative to said first and said second sources, and coaxial transmission-line means connecting said sources and said utilization means, said transmisionline means including rotary coupling means defining axially-spaced junctions between relatively rotatable inner and outer conductors, respectively, filter means associated v with` one said junction adapted to pass freely energy of both said frequencies and filter means associated with the other said junction adapted to pass waves of a predetermined one of said frequencies, and output coupling means connected to said transmission-line means to opposite sides of said last-named lter means for conducting energy. ofirespective ones of said frequencieszto said Hutilization'ameans.

4. Ay dual-channel'high-frequency'rotatable joint, com# prisinga transmission line section having relatively rotatable parts, axially-spaced means on one said part coupling energy: sources of different frequency values to said transmission line, `axially-spaced means yon the other part coupling saidv transmission line to utilization means loperable at said different frequencies, Wave-filter means on each said part and positioned between the spaced coupling means thereon, said filter means being adapted to selectively pass only -one of said frequencies, thereby effectively isolating the coupling means on each part with respect to the energy of said one of saidfrequencies, and additional filter'means at the junetion'fbetv/een-said relatively movable. parts, adaptedf to pass both said frequencies, thereby to minimize losses through said junc- OII;

5. In'multiple channel transmission apparatus, means defining` a path for the transmission of wave energy, a first filter, means obstructing the passage of wave energy at a first predetermined range vof frequencies in a first region of` said path, a second filter means obstructing the passage of wave. energy at said first predetermined range of frequencies in a second region of said path spaced from said first region, first and second energy transfer devices connected with said path respectively on either side of the region embraced'by said first `and second lter means, and third and fourth energy transfer devices connected in energy exchanging relationship with said path within the region defined by said first and second filter means, saidthird and fourth energy transfer devices having the property of effectively transferring. only wave energy characterized by a frequency exceeding a predetermined value, said predetermined value being less than that of the lowest frequency in said first predetermined range.

6. The combination according to claim 5, in which said path is defined by a pair of substantially coaxially disposed conductive members.

7. The combination `according to claim 5, in which the members defining different portions of said path are relatively rotatable.

8. In'a multiple channel device for transferring electromagnetic energy, means defining avpath for the trans mission of wave energy characterized by a first mode of energy propagation, a first filter means obstructing the passage of wave energy at a first predetermined range of frequencies disposed'in a first region of said path, a second filter means obstructing the passage of wave energy at said first predetermined range of frequencies in a. secondi region of saidV path spaced from said first region, first and second'energy transfer devices connected with saidwpath respectively on eitherV side of the region embraced by said first and second filter means, and third Iand fourth-mode transducing energy 'transfer devices connected inenergy exchanging relationship with said path within theregion'defined by said first and second filter means, said mode transducing devicesV translating the propagation mode of wave energy between saidfirst mode anda second mode characterized Iby a predetermined minimum propagation frequency, saidfminimum propagation frequency. being-g less thanithe lowest` frequency in saidrstpredetermined.range;

9; The.-combination according-,to'claim 8 i1rwhichltheI members defining different p ortionslof said path are.- relativelyfrotatable,

10. Infmultiplechannel transmission apparatus', a trans mission line comprising an inner conductor and an outer. conductor embracing.- said inner` conductor, first and second resonator chambers interposed in saidvouter conductor at spacedregions along. the length ofy said line, said resonators presenting animpedance maximum at a predetermined. frequency in theV sheath constituted by said outer; conductor, first and second transmission line. to waveguide couplers whose low frequency cut-ofi' is less than. said predeterminedfrequency connected with said line at spacedfpoints withinthe region definedfby` said resonator chambers, and third and. fourth` energyv transfer devices connected withv saidtransmissionlinerespectively 'at regions outside vthe region-bounded by said resonators.

1l. Theecombination according to claim l0, in which said transmission line to Wavev guide couplers are rigidly attached tosaid outer conductor and are relatively rotatable about a common axis contained within said outeri conductor.

12..The` combination accordingto claim 10, inwhich' said.. resonators are quarter wave resonant at said predetermined frequency.

13. In dual channel transmissiony apparatus, a transmission line comprising coaxially disposed jointedinnerl and outer conductors, a first pair of resonator-chambers spaced by one-half Wavelength on said transmission line. at a predetermined frequency interposed in said outer conductor, la second pair ofv resonator chambers spaced -by onefhalf wavelength on said transmission line at said predetermined frequency interposed in said outer conductor at a distance from said first pair,k said resonator chambers being quarter wave resonant to wave energy. yat said predeterminedfrequency, first and second transmission lineto wave guide couplers whose low frequency` cut-off is less than. said predetermined frequency connected with said line at spaced points within the region defined by said resonator chamber pairs, and means for making electrical connection with said transmission line` at locations disposed on either side of the region bounded. by said resonator chamber pairs, the sections of said line on either side of the joints being relatively rotatable. about the axis of said line.

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